The total resistance of displacement hull ships is composed primarily of frictional resistance at low speed/length ratios. As the speed and hence the speed/length ratio of these ships is increased the resistance increased dramatically. This dramatic increase in resistance is due mainly to the wave drag increase. For example the friction drag of a 400 foot (122 meter) LWL (Length Water Line) ship running at 15 knots makes up over 80 percent of total ship resistance. When that same ship is run at 45 knots this reverses and the wave drag makes up over 80 percent of total resistance. It is obvious that what needs to be done to be able to run displacement hulls at high speeds efficiently is to reduce wave drag.
Applicant has addressed this in some of his earlier filed applications wherein water for large waterjet propulsors is taken into propulsor water inlets located on the surface of bulbous bows with said water inlets disposed aft of the inward curving surface of the bulbous bows. The discharge water from the very large water propulsors used is, preferably, discharged into an air layer located on the underside of the ship's main hull. The effect of discharging the propulsor water into a pressurized air layer has several benefits. First, the discharge water jet is more efficient since there are no turbulent mixing losses related to the discharge water mixing with water flowing adjacent to the hull. Second, the air layer reduces frictional resistance of the hull. Third, it is possible to have a steering and/or reversing system installed on the discharge of the propulsor that is internal to the air layer and hence add no drag when moving forward at high speeds.
The instant invention carries that approach further and enhances the efficiency of the water inlets and therefore of the water propulsors themselves. This then also increases the related wave absorbing ability of the propulsors which reduces wave drag of the ship. This is accomplished in the first embodiment of the invention by having propulsor ram water inlet(s) disposed at the forward end of a secondary lower bow on the ship along with, optionally, water propulsor inlets at a forward knuckle and proximal the aft sides of the ship to maximize wave energy absorption. All propulsor water inlets are preferably supplied with Coanda effect fluid energy enhancers to further improve the efficiency of pressure recovery by the water propulsor inlets. Applicant has described such Coanda effect elements in an earlier application related to waterjet propulsors and they are also described in some detail in this application.
The instant invention offers advancements over applicant's earlier applications as well as over the prior art. These advancements are discussed in some detail in the following sections.